Revert #107376 to fix potential bincode breakage and rustc-perf benchmark.

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -330,6 +330,7 @@ fn compare_method_predicate_entailment<'tcx>(
  // lifetime parameters.
  let outlives_env = OutlivesEnvironment::with_bounds(
  param_env,
+ Some(infcx),
  infcx.implied_bounds_tys(param_env, impl_m_def_id, wf_tys.clone()),
  );
  infcx.process_registered_region_obligations(
@@ -727,6 +728,7 @@ pub(super) fn collect_return_position_impl_trait_in_trait_tys<'tcx>(
  // lifetime parameters.
  let outlives_environment = OutlivesEnvironment::with_bounds(
  param_env,
+ Some(infcx),
  infcx.implied_bounds_tys(param_env, impl_m_def_id, wf_tys),
  );
  infcx
@@ -2056,7 +2058,8 @@ pub(super) fn check_type_bounds<'tcx>(
  // Finally, resolve all regions. This catches wily misuses of
  // lifetime parameters.
  let implied_bounds = infcx.implied_bounds_tys(param_env, impl_ty_def_id, assumed_wf_types);
- let outlives_environment = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
+ let outlives_environment =
+ OutlivesEnvironment::with_bounds(param_env, Some(&infcx), implied_bounds);
 
  infcx.err_ctxt().check_region_obligations_and_report_errors(
  impl_ty.def_id.expect_local(),

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -115,7 +115,8 @@ pub(super) fn enter_wf_checking_ctxt<'tcx, F>(
  return;
  }
 
- let outlives_environment = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
+ let outlives_environment =
+ OutlivesEnvironment::with_bounds(param_env, Some(infcx), implied_bounds);
 
  let _ = infcx
  .err_ctxt()
@@ -675,6 +676,7 @@ fn resolve_regions_with_wf_tys<'tcx>(
  let infcx = tcx.infer_ctxt().build();
  let outlives_environment = OutlivesEnvironment::with_bounds(
  param_env,
+ Some(&infcx),
  infcx.implied_bounds_tys(param_env, id, wf_tys.clone()),
  );
  let region_bound_pairs = outlives_environment.region_bound_pairs();

compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs

@@ -179,7 +179,7 @@ fn get_impl_substs(
  }
 
  let implied_bounds = infcx.implied_bounds_tys(param_env, impl1_def_id, assumed_wf_types);
- let outlives_env = OutlivesEnvironment::with_bounds(param_env, implied_bounds);
+ let outlives_env = OutlivesEnvironment::with_bounds(param_env, Some(infcx), implied_bounds);
  let _ =
  infcx.err_ctxt().check_region_obligations_and_report_errors(impl1_def_id, &outlives_env);
  let Ok(impl2_substs) = infcx.fully_resolve(impl2_substs) else {

compiler/rustc_hir_typeck/src/pat.rs

@@ -238,8 +238,15 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
  // Note that there are two tests to check that this remains true
  // (`regions-reassign-{match,let}-bound-pointer.rs`).
  //
- // 2. An outdated issue related to the old HIR borrowck. See the test
+ // 2. Things go horribly wrong if we use subtype. The reason for
+ // THIS is a fairly subtle case involving bound regions. See the
+ // `givens` field in `region_constraints`, as well as the test
  // `regions-relate-bound-regions-on-closures-to-inference-variables.rs`,
+ // for details. Short version is that we must sometimes detect
+ // relationships between specific region variables and regions
+ // bound in a closure signature, and that detection gets thrown
+ // off when we substitute fresh region variables here to enable
+ // subtyping.
  }
 
  /// Compute the new expected type and default binding mode from the old ones

compiler/rustc_infer/src/infer/canonical/query_response.rs

@@ -636,9 +636,11 @@ pub fn make_query_region_constraints<'tcx>(
  outlives_obligations: impl Iterator<Item = (Ty<'tcx>, ty::Region<'tcx>, ConstraintCategory<'tcx>)>,
  region_constraints: &RegionConstraintData<'tcx>,
 ) -> QueryRegionConstraints<'tcx> {
- let RegionConstraintData { constraints, verifys, member_constraints } = region_constraints;
+ let RegionConstraintData { constraints, verifys, givens, member_constraints } =
+ region_constraints;
 
  assert!(verifys.is_empty());
+ assert!(givens.is_empty());
 
  debug!(?constraints);
 

compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs

@@ -13,7 +13,7 @@ use rustc_data_structures::graph::implementation::{
  Direction, Graph, NodeIndex, INCOMING, OUTGOING,
 };
 use rustc_data_structures::intern::Interned;
-use rustc_index::vec::IndexVec;
+use rustc_index::vec::{Idx, IndexVec};
 use rustc_middle::ty::fold::TypeFoldable;
 use rustc_middle::ty::PlaceholderRegion;
 use rustc_middle::ty::{self, Ty, TyCtxt};
@@ -132,6 +132,7 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
  }
 
  let graph = self.construct_graph();
+ self.expand_givens(&graph);
  self.expansion(&mut var_data);
  self.collect_errors(&mut var_data, errors);
  self.collect_var_errors(&var_data, &graph, errors);
@@ -163,6 +164,38 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
  }
  }
 
+ fn expand_givens(&mut self, graph: &RegionGraph<'_>) {
+ // Givens are a kind of horrible hack to account for
+ // constraints like 'c <= '0 that are known to hold due to
+ // closure signatures (see the comment above on the `givens`
+ // field). They should go away. But until they do, the role
+ // of this fn is to account for the transitive nature:
+ //
+ // Given 'c <= '0
+ // and '0 <= '1
+ // then 'c <= '1
+
+ let seeds: Vec<_> = self.data.givens.iter().cloned().collect();
+ for (r, vid) in seeds {
+ // While all things transitively reachable in the graph
+ // from the variable (`'0` in the example above).
+ let seed_index = NodeIndex(vid.index() as usize);
+ for succ_index in graph.depth_traverse(seed_index, OUTGOING) {
+ let succ_index = succ_index.0;
+
+ // The first N nodes correspond to the region
+ // variables. Other nodes correspond to constant
+ // regions.
+ if succ_index < self.num_vars() {
+ let succ_vid = RegionVid::new(succ_index);
+
+ // Add `'c <= '1`.
+ self.data.givens.insert((r, succ_vid));
+ }
+ }
+ }
+ }
+
  /// Gets the LUb of a given region and the empty region
  fn lub_empty(&self, a_region: Region<'tcx>) -> Result<Region<'tcx>, PlaceholderRegion> {
  match *a_region {
@@ -329,6 +362,18 @@ impl<'cx, 'tcx> LexicalResolver<'cx, 'tcx> {
  ) -> bool {
  debug!("expand_node({:?}, {:?} == {:?})", a_region, b_vid, b_data);
 
+ match *a_region {
+ // Check if this relationship is implied by a given.
+ ty::ReEarlyBound(_) | ty::ReFree(_) => {
+ if self.data.givens.contains(&(a_region, b_vid)) {
+ debug!("given");
+ return false;
+ }
+ }
+
+ _ => {}
+ }
+
  match *b_data {
  VarValue::Empty(empty_ui) => {
  let lub = match self.lub_empty(a_region) {

compiler/rustc_infer/src/infer/mod.rs

@@ -855,6 +855,10 @@ impl<'tcx> InferCtxt<'tcx> {
  self.inner.borrow().undo_log.opaque_types_in_snapshot(&snapshot.undo_snapshot)
  }
 
+ pub fn add_given(&self, sub: ty::Region<'tcx>, sup: ty::RegionVid) {
+ self.inner.borrow_mut().unwrap_region_constraints().add_given(sub, sup);
+ }
+
  pub fn can_sub<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool
  where
  T: at::ToTrace<'tcx>,

compiler/rustc_infer/src/infer/outlives/env.rs

@@ -1,9 +1,9 @@
 use crate::infer::free_regions::FreeRegionMap;
-use crate::infer::GenericKind;
+use crate::infer::{GenericKind, InferCtxt};
 use crate::traits::query::OutlivesBound;
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_data_structures::transitive_relation::TransitiveRelationBuilder;
-use rustc_middle::ty::{self, Region};
+use rustc_middle::ty::{self, ReEarlyBound, ReFree, ReVar, Region};
 
 use super::explicit_outlives_bounds;
 
@@ -75,7 +75,7 @@ impl<'tcx> OutlivesEnvironment<'tcx> {
  region_bound_pairs: Default::default(),
  };
 
- builder.add_outlives_bounds(explicit_outlives_bounds(param_env));
+ builder.add_outlives_bounds(None, explicit_outlives_bounds(param_env));
 
  builder
  }
@@ -89,10 +89,11 @@ impl<'tcx> OutlivesEnvironment<'tcx> {
  /// Create a new `OutlivesEnvironment` with extra outlives bounds.
  pub fn with_bounds(
  param_env: ty::ParamEnv<'tcx>,
+ infcx: Option<&InferCtxt<'tcx>>,
  extra_bounds: impl IntoIterator<Item = OutlivesBound<'tcx>>,
  ) -> Self {
  let mut builder = Self::builder(param_env);
- builder.add_outlives_bounds(extra_bounds);
+ builder.add_outlives_bounds(infcx, extra_bounds);
  builder.build()
  }
 
@@ -119,7 +120,12 @@ impl<'tcx> OutlivesEnvironmentBuilder<'tcx> {
  }
 
  /// Processes outlives bounds that are known to hold, whether from implied or other sources.
- fn add_outlives_bounds<I>(&mut self, outlives_bounds: I)
+ ///
+ /// The `infcx` parameter is optional; if the implied bounds may
+ /// contain inference variables, it must be supplied, in which
+ /// case we will register "givens" on the inference context. (See
+ /// `RegionConstraintData`.)
+ fn add_outlives_bounds<I>(&mut self, infcx: Option<&InferCtxt<'tcx>>, outlives_bounds: I)
  where
  I: IntoIterator<Item = OutlivesBound<'tcx>>,
  {
@@ -136,14 +142,27 @@ impl<'tcx> OutlivesEnvironmentBuilder<'tcx> {
  self.region_bound_pairs
  .insert(ty::OutlivesPredicate(GenericKind::Alias(alias_b), r_a));
  }
- OutlivesBound::RegionSubRegion(r_a, r_b) => match (*r_a, *r_b) {
- (
- ty::ReStatic | ty::ReEarlyBound(_) | ty::ReFree(_),
- ty::ReStatic | ty::ReEarlyBound(_) | ty::ReFree(_),
- ) => self.region_relation.add(r_a, r_b),
- (ty::ReError(_), _) | (_, ty::ReError(_)) => {}
- _ => bug!("add_outlives_bounds: unexpected regions"),
- },
+ OutlivesBound::RegionSubRegion(r_a, r_b) => {
+ if let (ReEarlyBound(_) | ReFree(_), ReVar(vid_b)) = (r_a.kind(), r_b.kind()) {
+ infcx
+ .expect("no infcx provided but region vars found")
+ .add_given(r_a, vid_b);
+ } else {
+ // In principle, we could record (and take
+ // advantage of) every relationship here, but
+ // we are also free not to -- it simply means
+ // strictly less that we can successfully type
+ // check. Right now we only look for things
+ // relationships between free regions. (It may
+ // also be that we should revise our inference
+ // system to be more general and to make use
+ // of *every* relationship that arises here,
+ // but presently we do not.)
+ if r_a.is_free_or_static() && r_b.is_free() {
+ self.region_relation.add(r_a, r_b)
+ }
+ }
+ }
  }
  }
  }

compiler/rustc_infer/src/infer/region_constraints/leak_check.rs

@@ -424,6 +424,9 @@ impl<'tcx> MiniGraph<'tcx> {
  &AddConstraint(Constraint::RegSubReg(a, b)) => {
  each_edge(a, b);
  }
+ &AddGiven(a, b) => {
+ each_edge(a, tcx.mk_re_var(b));
+ }
  &AddVerify(i) => span_bug!(
  verifys[i].origin.span(),
  "we never add verifications while doing higher-ranked things",

compiler/rustc_infer/src/infer/region_constraints/mod.rs

@@ -7,7 +7,7 @@ use super::{
  InferCtxtUndoLogs, MiscVariable, RegionVariableOrigin, Rollback, Snapshot, SubregionOrigin,
 };
 
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxIndexSet};
 use rustc_data_structures::intern::Interned;
 use rustc_data_structures::sync::Lrc;
 use rustc_data_structures::undo_log::UndoLogs;
@@ -104,6 +104,26 @@ pub struct RegionConstraintData<'tcx> {
  /// An example is a `A <= B` where neither `A` nor `B` are
  /// inference variables.
  pub verifys: Vec<Verify<'tcx>>,
+
+ /// A "given" is a relationship that is known to hold. In
+ /// particular, we often know from closure fn signatures that a
+ /// particular free region must be a subregion of a region
+ /// variable:
+ ///
+ /// foo.iter().filter(<'a> |x: &'a &'b T| ...)
+ ///
+ /// In situations like this, `'b` is in fact a region variable
+ /// introduced by the call to `iter()`, and `'a` is a bound region
+ /// on the closure (as indicated by the `<'a>` prefix). If we are
+ /// naive, we wind up inferring that `'b` must be `'static`,
+ /// because we require that it be greater than `'a` and we do not
+ /// know what `'a` is precisely.
+ ///
+ /// This hashmap is used to avoid that naive scenario. Basically
+ /// we record the fact that `'a <= 'b` is implied by the fn
+ /// signature, and then ignore the constraint when solving
+ /// equations. This is a bit of a hack but seems to work.
+ pub givens: FxIndexSet<(Region<'tcx>, ty::RegionVid)>,
 }
 
 /// Represents a constraint that influences the inference process.
@@ -277,6 +297,9 @@ pub(crate) enum UndoLog<'tcx> {
  /// We added the given `verify`.
  AddVerify(usize),
 
+ /// We added the given `given`.
+ AddGiven(Region<'tcx>, ty::RegionVid),
+
  /// We added a GLB/LUB "combination variable".
  AddCombination(CombineMapType, TwoRegions<'tcx>),
 }
@@ -325,6 +348,9 @@ impl<'tcx> RegionConstraintStorage<'tcx> {
  self.data.verifys.pop();
  assert_eq!(self.data.verifys.len(), index);
  }
+ AddGiven(sub, sup) => {
+ self.data.givens.remove(&(sub, sup));
+ }
  AddCombination(Glb, ref regions) => {
  self.glbs.remove(regions);
  }
@@ -466,6 +492,15 @@ impl<'tcx> RegionConstraintCollector<'_, 'tcx> {
  self.undo_log.push(AddVerify(index));
  }
 
+ pub(super) fn add_given(&mut self, sub: Region<'tcx>, sup: ty::RegionVid) {
+ // cannot add givens once regions are resolved
+ if self.data.givens.insert((sub, sup)) {
+ debug!("add_given({:?} <= {:?})", sub, sup);
+
+ self.undo_log.push(AddGiven(sub, sup));
+ }
+ }
+
  pub(super) fn make_eqregion(
  &mut self,
  origin: SubregionOrigin<'tcx>,
@@ -769,8 +804,11 @@ impl<'tcx> RegionConstraintData<'tcx> {
  /// Returns `true` if this region constraint data contains no constraints, and `false`
  /// otherwise.
  pub fn is_empty(&self) -> bool {
- let RegionConstraintData { constraints, member_constraints, verifys } = self;
- constraints.is_empty() && member_constraints.is_empty() && verifys.is_empty()
+ let RegionConstraintData { constraints, member_constraints, verifys, givens } = self;
+ constraints.is_empty()
+ && member_constraints.is_empty()
+ && verifys.is_empty()
+ && givens.is_empty()
  }
 }
 

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -388,6 +388,7 @@ fn resolve_negative_obligation<'tcx>(
  let wf_tys = ocx.assumed_wf_types(param_env, DUMMY_SP, body_def_id);
  let outlives_env = OutlivesEnvironment::with_bounds(
  param_env,
+ Some(&infcx),
  infcx.implied_bounds_tys(param_env, body_def_id, wf_tys),
  );
 

compiler/rustc_trait_selection/src/traits/misc.rs

@@ -111,6 +111,7 @@ pub fn type_allowed_to_implement_copy<'tcx>(
  // Check regions assuming the self type of the impl is WF
  let outlives_env = OutlivesEnvironment::with_bounds(
  param_env,
+ Some(&infcx),
  infcx.implied_bounds_tys(
  param_env,
  parent_cause.body_id,

compiler/rustc_trait_selection/src/traits/outlives_bounds.rs

@@ -3,8 +3,7 @@ use crate::traits::query::type_op::{self, TypeOp, TypeOpOutput};
 use crate::traits::query::NoSolution;
 use crate::traits::ObligationCause;
 use rustc_data_structures::fx::FxIndexSet;
-use rustc_infer::infer::resolve::OpportunisticRegionResolver;
-use rustc_middle::ty::{self, ParamEnv, Ty, TypeFolder, TypeVisitableExt};
+use rustc_middle::ty::{self, ParamEnv, Ty};
 use rustc_span::def_id::LocalDefId;
 
 pub use rustc_middle::traits::query::OutlivesBound;
@@ -53,10 +52,6 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
  body_id: LocalDefId,
  ty: Ty<'tcx>,
  ) -> Vec<OutlivesBound<'tcx>> {
- let ty = self.resolve_vars_if_possible(ty);
- let ty = OpportunisticRegionResolver::new(self).fold_ty(ty);
- assert!(!ty.needs_infer());
-
  let span = self.tcx.def_span(body_id);
  let result = param_env
  .and(type_op::implied_outlives_bounds::ImpliedOutlivesBounds { ty })
@@ -110,7 +105,10 @@ impl<'a, 'tcx: 'a> InferCtxtExt<'a, 'tcx> for InferCtxt<'tcx> {
  tys: FxIndexSet<Ty<'tcx>>,
  ) -> Bounds<'a, 'tcx> {
  tys.into_iter()
- .map(move |ty| self.implied_outlives_bounds(param_env, body_id, ty))
+ .map(move |ty| {
+ let ty = self.resolve_vars_if_possible(ty);
+ self.implied_outlives_bounds(param_env, body_id, ty)
+ })
  .flatten()
  }
 }